Various types of couplings and other torque transmitters have been used in many applications for connecting input and output shafts. Generally, such devices have been substantially locked as the two shafts rotate, such that torsional vibrations or shocks on the input or output shafts are transmitted to the other shaft, many times with amplification, as well as to other component parts of the apparatus. The present invention is directed to an energy-absorbing torque transmitter that is a cushioning device, that is, a torsional shock absorber and, therefore, torsional vibrations are largely absorbed and not substantially transmitted from one shaft to the other. For example, in automotive vehicles that make use of an automatic transmission it may be desirable to include a lock-up clutch to directly couple engine drive shaft to transmission input shaft when the vehicle reaches a certain speed. Its purpose is to eliminate fuel losses related to torque converter slip. If the shafts are rigidly locked by this clutch, torsional vibrations or shocks on either shaft are transmitted to the other as well as to the rest of the vehicle and its occupants. A torque cushioning device within the clutch is therefore desirable. Such a torque cushion must handle full engine torque, and any fractional part thereof, plus and minus the torsional vibrations derived from cyclic engine firing and other changes in demand load by the wheels. The softer the cushion the lower will be its natural frequency, and the better it will be for shock and vibration damping.
Compression spring systems have been used for the torque cushioning portion of the lock-up clutch in an automotive vehicle, but their very presence, i.e., the space they occupy, plus their necessary push rods, severely limits the amount of differential rotation permitted between the two shafts. Such systems are hard cushions with correspondingly high natural frequencies of vibration and, therefore, they perform poorly in response to sudden power surges and do little toward the damping of external vibrations.
The present invention is particularly suitable for use in automatic transmissions in automotive vehicles since it provides a means for substantially eliminating vibrations and shock due to power surges from the engine, misfires and sudden changes in demand load for propulsion. In an automatic transmission the present invention provides for substantially eliminating fluid slip in the torque converter. Fluid slip results in energy loss, and thence, in heat buildup and excess fuel consumption. Thus the present invention, when used in automotive vehicles equipped with automatic transmissions, can result in substantially lower fuel consumption. Also, the apparatus described herein, when used as an energy-absorbing torque cushion, offers a lower natural frequency of vibration compared to metal spring system farther removed from the range of frequencies associated with automotive engines, drive shaft, gear and the like and, therefore, results in a smoother riding vehicle. Although the apparatus of the present invention will be described primarily in relation to a lock-up clutch in an automatic transmission for an automotive vehicle it can be used in other applications.